Call Northside 777 (1948)
This film directed by Henry Hathaway is an outstanding example of what Hollywood could do when it wanted to.
The cast is perfect for the task of presenting a gripping story taken from a true life incident and has a terrific script that perfectly matches the action. James Stewart is superb as the cynical reporter who is directed by his editor, played brilliantly by Lee J Cobb, to follow up an 11 year murder of a police officer. Everyone concerned in the making of this film created one of the USA's best crime stories ever filmed.
Here's the opening:
http://youtu.be/P1YYgkfoFBE